6-indirectretainers-200630121301.pdf

cast partial denture

1. INDIRECT RETAINERS
IN REMOVABLE PARTIAL
DENTURES
BY: Dr. Prathamesh Fulsundar
(MDS –Prostodontics)

2. Contents
Introduction
Definition of indirect retainer
Function of indirect retainer
Fulcrum lines
Effect of rotational movement
Factors determining effectiveness of indirect retainers
Types of indirect retainer
Conclusion
References

3. INDIRECT RETAINERS

4. A RPD derives support from two main sources
periodontallysound natural teeth& residual alveolar
processes and associated soft tissues.
A RPD that is supported by healthy natural teeth
possesses adequate stability and retention to resist
functional displacement.
However, a RPD that is not entirely bounded by natural
teeth will move when a load is applied.
INTRODUCTION

5. TYPES OF LEVER
Mechanical Advantage= EffortArm
ResistanceArm

6. PRINCIPLEOF INDIRECT
RETENTINERS

7. DEFINITION
The component of a removable partial denture that assists
the direct retainer in preventing displacement of the distal
extension denture base by functioning through lever action
on the opposite side of the fulcrum linewhen the denture
base attempts to move away from the tissues in pure
rotation around the fulcrum line. (GPT 9)

8. FUNCTIONS OF INDIRECT
RETAINERS
Reduces the antero-posterior twisting
Helps in stabilization
Acts as an auxiliary guiding plane.
It splintsthe anterior tooth against lingual movement.
May act as auxiliary rest to support major connector.
It counteracts horizontal forces.
It provides lateral stability.
May provide first indicationto reline an extension base.
It acts as a third point for contacting the tooth structure to ensure
accurate repositioning of the frame work on the tooth during
rebasing and relining.

9. Afulcrum lineis an imaginary
linearound which anRPDwill tend
to rotate.
When an occlusal load is applied
to a distal extension removable
partial denture, the prosthesis
rotates around a fulcrum line that
passes through the most posterior
rests one on each side of the
dental arch
Displacement of the prosthesis is
limited by the hard and soft tissues
of the residual ridge.
FULCRUM LINE

10. Active tissues such as the tongue and buccinator
muscle also may displace the denture base during
speech, mastication, or swallowing.
When a distal extension removable partial denture is
subjected to such forces, the associated fulcrum line
passes through the tipsof the retentive clasps.

11. EFFECT OF ROTATIONAL
MOVEMENT
When the posterior portion of a Kennedy Class I or
Class II removable partial denture is subjected to
occlusallydirected dislodging forces in the absence of
properly designed indirect retention, two undesirable
events occur:
(1) The denture base movesawayfrom the supporting
tissues.
(2) The anterior segment of the major connector impinges
upon the underlying soft tissues.

12. Concept of indirect retention was originally advocated
by Dr. W. E. Cummeras a means of resisting rotational
displacement.
When in positive contact with a rest seat, an indirect
retainer contributes to the overall support and stability of
the removable partial denture.
For a long-span lingual bar, properly constructed indirect
retainers can provide additional support and rigidity to
the major connector.

13. FULCRUM LINES FOUND IN VARIOUS
TYPES OF PARTIALLY EDENTULOUS
ARCHES
Class I arch
The fulcrum line passes through the most posterior
abutments, provided some rigid component of the framework
is occlusal to the abutment’s heights of contour.

14. Class II arch
The fulcrum line is diagonal, passing through the abutment
on the distal extension side and the most posterior
abutmenton the opposite side.

15. In a Class III arch
Indirect retention may not be needed as it is tooth supported.
However in cases with non supporting posterior teeth, the
adjacent edentulous area is considered to be the tissue-
supported end, with a diagonal fulcrum line passing through
the two principal abutments, as in a Class II arch.

16. Class IV arch
The fulcrum line passes through two abutments adjacent
to the single edentulous space.

17. FACTORS DETERMINING
EFFECTIVENESS
OF INDIRECT RETAINERS
1.The principal occlusal rests on the primary abutment teeth
must be reasonably held in their seats by the retentive
arms of the direct retainers.
2. The following three areas must be considered:
Lengthof the distal extension base
Locationof the fulcrum line
Distancefrom the fulcrum line

18. 3. The connectors supporting the indirect retainer must be
rigid.
4. Effectiveness of the supporting tooth surface
The indirect retainer must be placed on a definite rest
seat on which slippage or tooth movement will not occur.
The Tooth inclines and weak teeth should neverbe used
to support indirect retainers.

19. TYPES OF INDIRECT
RETAINERS
1.Auxiliary Occlusal Rest
2.Canine Extension From The Occlusal Rest
3.Canine Rest
4.Continuous Bar Retainers And Linguo-plates
5.Modification Areas
6.RugaeSupport
7.Direct Indirect Retension
8.Indirect Retention From Major Connector
9.IncisalRest
10.EmbrassureHook
11.Double Lingual Bar Or Kennedy’s Bar

20. 1-AUXILIARY OCCLUSAL REST
-Most frequently used.
-Located on the occlusal surface far away from distal
extension denture base.
-It is placed perpendicularto the midpoint of the fulcrum line.
-Ideal location is central incisor, which is weak, therefore
bilateral rests on first premolars are effective.
-Rests on premolars do not interfere with tongue movements.
In Kenneddy’sclass1
-Bilateral rests on mesialfossaof
first premolars.
In Kenneddy’sclass2
-Mesialfossaof first premolar on
opposite side.

21. PREPARATION OF OCCLUSAL REST
Rounded triangle
Base at the marginal ridge and apex at
the centre of thetooth
One-half the intercuspaldistance and
one-third/one-half the mesiodistal
width
Base must be less than 90
0
to long axis
oftooth.
Depth 0.5 at the thinnest portion and
1.5mm at the marginalridge.

22. 2-CANINE EXTENSION FROM THE OCCLUSAL REST
-Consists of a finger extension from premolar rest to the
lingual slope of adjacent canine.
-Used when first premolar is the primary abutment.
-This design avoids the tipping action produced in a single
cingulamcanine rest.

23. 3-CANINE REST(CINGULUM REST or LINGUAL REST)
•Canine rest is used when mesialmarginal ridge of the
1st premolar is too close to the fulcrum line.
•Lingual rest is prepared mostly on maxillary canines
•Rest seat are V shape & half moon shape.

24. 4-CONTINUOUS BAR RETAINERS & LINGUO -PLATES
As they rest on unprepared lingual surfaces they aid the
terminal rests by providing indirect retention.
They also help to splint weaker anterior teeth.
A continuous bar retainer or superior border of the linguo-
plate should never be placed above the middle third of
the teeth to avoid tooth movement (kennedyclass1 & 2).

25. 5-MODIFICATION AREAS
The occlusal rest on a secondary abutment in class 2
modification 1 serve as an indirect retainer.
If only one tooth is missing in the modification areas,
occlusal rest on this side should provide support for
the unsupported major connector along with indirect
retention.

26. 6-RUGAE SUPPORT
Rugaearea is firm hence used for indirect retention
espciallyfor class I situations.
Used for indirect retention for palatal horseshoe major
connector.
Less effective than a tooth supported indirect retainer.

27. 7-DIRECT INDIRECT RETENSION
Reciprocal arm of a direct retainer located anterior to
fulcrum line may act as indirect retainer.

28. 8-INDIRECT RETENTION FROM MAJOR CONNECTORS
In mandible, retention from denture base itself help in
indirect retention.
In maxillary arch ,full palatal coverage is necessary for
additional indirect retention.
It is obtained from major connector’s resistance to
distortion.

29. 9-INCISAL REST
On mandibular canines when mesialfossaof 1st
premolar is close to fulcrum line.

30. 10-EMBRASSURE HOOK
Less desirable, which engages anterior inter
proximalareas.
Used when less positive seat to stabilize the
indirect retainer.
Unaestheticdue to metallic display.

31. 11-DOUBLE LINGUAL BAR OR KENNEDY’S BAR
Less effective.
It rests on unprepared lingual surface, thus
enhancing the indirect retention at terminal rests.
It is extended far from fulcrum line.

32. CONCLUSION
Proper designing the connector for the partial
edentulous space is necessary to perform function.
It is important for clinician to understand the possible
movements in response to function and help control
these movements.

33. REFERENCES
Clinical removable partial prosthodontics-stewartrudd
kuebker-2nd EDITION
Mccracken'sRemovable Partial Prosthodontics-alan
B.Carr, glen P.Mcgivney,davidT.Brown-11th Edition.
Ernest L.Millerand Joseph E.Grasso,RemovablePartial
Prosthodontics, ed2. 1979,Williams andWillkins.
A.A.Grantand W.Johnson,Removabledenture
Prosthodontics, ed2.1992,Churchill livingstoneInc.
William E. Avant.Indirectretention In partial denture
Design.JProsthetDent.16:1103-1110
The glossary of prosthodonticterms

34. Thank you